Generally, a hall is equipped with a plurality of game machines for pachinko game, pachislo game, etc. Each game machine in this hall is constructed so that a game is started with throwing of a game medium such as a pachinko ball or medal, and the game medium is paid out corresponding to the winning state (style) occurred in the course of the game.
This game machine is set such that a winning state occurs at a preset probability. Therefore, the player continues the game in expectation of a prize.
In the game machine that produces a prize merely depending on the probability as described, the probability of prize converges on the preset probability by performing a significant number of games. Accordingly, there is the following occasions: i) a player performing a small number of games has the fortune to get a prize before long; and ii) every player performing a large number of games is not reserved for prize. With the game machine of this type, gambling characteristics can be enhanced to make the game more amusing. On the other hand, the player waiting for a prize for a long time might lose enthusiasm for the game and keep away from the hall (i.e., a reduction in the number of customers).
In order to solve the above disadvantage, for example, there has been proposed the following techniques of: i) controlling return rates to game machines such that the average of the returns rates to all the game machines has a predetermined value (Japanese Patent Unexamined Publication No. 6-79051); and ii) adjusting the probability of prize in consideration of the profit rate of a hall and the return rate to players (Japanese Patent Unexamined Publication No. 11-253640). However, the techniques disclosed in these publications are still not directed to guarantee a return to players, although the players will suffer no unfairness by eliminating variations in the probability of a big prize per game machine.
As a typical slot game machine (slot machine), there is one that employs the following technique: i) depending on the consumed number of games, the probability of a big prize is changed so as to produce the big prize more frequently (Japanese Patent Unexamined Publication No. 8-24401); or ii) the probability of prize on a reel slot is controlled to be changed depending on the medal payout rate during the past certain period of time (Japanese Patent Unexamined Publication No. 11-146938). With the slot game machines employing the above technique disclosed in these publications, the probability of a big prize is increased depending on the consumed number of games. This burdens on a hall controlling a plurality of game machines. As the result, a reduction in the total returnable amount is unavoidable. In other words, the techniques in these publications are not directed to guarantee a return to players.
As a typical medal game machine, there is one that employs a technique of paying out a predetermined number of medals per game machine, when a predetermined wining-prize character occurs (Japanese Patent Unexamined Publication No. 10-118247). However, this medal game machine is set such that the player can receive a profit of bonus when a specific wining-prize character occurs. Therefore, this machine is not directed to guarantee a return to players.
In a casino hall where a plurality of slot machines are disposed, part of credit consumed by every slot machine is reserved. When the amount of reservation reaches a certain sum of money, there is moved to the so-called “jackpot” mode that an exceedingly large amount is paid out to a certain slot machine. Concretely, every slot machine is set so as to produce a prize at a preset probability in the normal mode. Therefore, the player continues a game in expectation of a prize. In the meantime, the jackpot occurs on a certain slot machine at a given timing by lottery that is different from the usual prize lottery based on a preset probability set on the slot machines. In the case that the jackpot is so produced on a certain slot machine only, the sum of money obtained by the jackpot is extremely large. Such gambling characteristics can make the game more interest, whereas the probability of jackpot is extremely low, thereby failing to guarantee a return depending on the sum of money that the player throws in.